Bowers & Wilkins 702 S2 loudspeaker

Late in the summer of 2015, I was one of the press representatives invited by Bowers & Wilkins to visit their R&D center in Steyning, West Sussex, England, and be given a detailed preview of the upcoming revision of their entire 800 series of loudspeaker models. Both the technical presentation and the tours impressively demonstrated the comprehensive redesign process that resulted in speakers that were superficially similar but entirely different from their predecessors. Of the new series, I reviewed the 802 D3 Diamond, a pair of which now sit in my listening room as my current reference speakers.

In late summer 2017, following the sale of Bowers & Wilkins to EVA Automation, a group of US press were invited to B&W's US office, which was then near Boston, for a presentation intended to reassure the audio world that B&W would continue to produce the sorts of products that had brought the company to prominence. What was presented was an entirely new series of loudspeakers: the 700 S2 models. The original 700 series, priced between the flagship 800 and midpriced 600 series, had disappeared some years before, that slot filled in 2008 by the CM series. But from the get-go, the CM models seemed a discontinuity in B&W's product line. To me, the CMs seemed like somewhat glitzy adaptations of the 600 series, and had too little in common with the 800 series. Happily, the new 700 S2 line is a more suitable replacement for the old 700 line.

The presentation by Andy Kerr, B&W's senior product manager, was strikingly similar to the one he'd organized in 2015 for the 800 D3 seriesand, unlike the CMs, the new 700 S2s are admittedly and obviously derived from the new 800 models. The biggest differences between new 800 and new 700 speakers are in their cabinet construction and where they're madedifferences that probably account for most of the significant differences in price. The traditional rectangular enclosures of the floorstanding 700 S2 models are undoubtedly much less expensive to make than their 800 D3 counterparts' curved, one-piece, multilaminate cabinets topped with Turbine midrange enclosures of machined aluminum and supported by plinths of solid aluminum. The 700 S2 series is also the first range of conventional B&W speakers has manufactured in their new factory in Zhuhai, China. The only speakers B&W still manufactures in their Worthing, Sussex factory are the 800 D3 models and the iconic Nautilus.

Description
I summarized the technical features of the 700 S2 series in "Industry Update" in the November 2017 issue (p.15). The highlights include: 1) a carbon-dome tweeter with the same construction and motor as the diamond dome in the 800 D3 line, and, in two models, a solid-body, bullet-shaped tweeter enclosure of machined aluminum reengineered from the 800 D3s to better fit the 700 S2s' rectangular cabinets; 2) the 800 D3s' silvery Continuum cone for the 700 S2s' midrange and midrange/woofer; 3) for the midrange drivers, front-panel decoupling and a tuned-mass damper derived from the 800 D3s; 4) an Aerofoil-profile laminate for the woofer diaphragms, but with the foam core covered by a skin of paper rather than carbon; and 5) reengineered cast baskets for the midrange drivers, for greater stiffness and damping.

The names of the 700 S2 models parallel those of the 800 D3s in regard to size, floorstanding vs stand-mounted, and two- vs three-way. I quickly made a bid to review the top model, the 702 S2 ($4500/pair). The largest three-way model in the line, it features the external bullet housing for the tweeter.

In the Rosenut finish of my review samples, the 702 S2 is a gracefully proportioned, beautifully finished loudspeaker, and the piano-black-and-silver housing for its 1" decoupled carbon-dome tweeter adds a dash of panache. Vertically arrayed below the tweeter are a 6" woven Continuum- cone FST midrange unit and three 6.5" Aerofoil Profile woofers; the fine silver details surrounding their diaphragms give the speaker an elegant appearance even without its black grille. On the rear panel is B&W's dimpled, tapered Flowport, and just below that is a shallow bay containing four multiway speaker terminals suitable for biwiring. (Jumpers are provided, but I biwired.) Included with the 702 S2 is an optional-use plinth that widens the speaker's stance for greater stability. B&W provides adjustable spikes and feet, either of which can be attached to the plinth or directly to the speaker's bottom panel.

After removing the little foam strips that prevent the tweeter housing from moving during shipment, I put the 702 S2s in the front of my room and experimented a bit with their positions. I found placement relatively uncritical, but I never tried them closer to any wall than about 2'. They ended up 34' from the sidewalls, 6' from the wall behind them, about 10.5' from my listening seat, 7.5' apart, and toed in about 20°. That was a little closer to each other and to me than I'd had the 802 D3s, but with similar orientation. By the time that was done, I'd gotten over my initial surprise at the 702 S2s' uncommonly clean sound and lack of room boom.

Partnering
I began by powering the B&W 702 S2s with two Classé Sigma Mono monoblocks (350W into 8 ohms), and after a while switched to using two channels of a Parasound Halo A 31 three-channel amp (250Wpc into 8 ohms). Each arrangement provided more than enough power, the Classé Sigmas slightly exceeding B&W's recommendation of 30300W per speaker. It was with the Classés that I latched on to the 702 S2s' overall balance and excellent imaging, but I soon heard inklings of some weakness in the upper bass. I anticipated that the Parasound might cure this, and it did, but only partly.

Eventually, I came to realize that I'd been treating the 702 S2s with kid gloves by playing them at lower levels than I usually enjoy. Y'see, even though the volume knob was where I usually keep it, that setting is appropriate for how I mostly listen to music: in surround sound, with five amps driving five speakers. But now I was listening to only two channels, and of course I had to turn it up. Duh.

Bingo! A simple tweak of the knob erased all my concerns about the bass. Michael McDonald was back to his old self, as were Hans Theesink, Leonard Cohen, and operatic bass Gottlob Frick. That was with either the Classé Sigma Monos or the Parasound Halo A 31but I slightly preferred the sound of the 702 S2s with the Parasound.

I listened both with and without the speakers' grilles in placemostly with, as I heard no difference.

Listening
I began with Poulenc's Violin Sonata, electrifyingly played by Patricia Kopatchinskaja and pianist Polina Leschenko (CD, Alpha 387). It begins slam-bang, with a forceful piano chord and a violin swoop, and I was immediately aware of two things. First, while my own dad was Poulenc's contemporary, this is not your father's idea of chamber musicit was brilliant, witty, romantic, and at times wistful. Second, the chord and the swoop were right there, about 2' behind the plane described by the 702 S2s' baffles, with just enough space for the two instruments to blend with my room's acoustic and create a convincing illusion that Kopatchinskaja and Leschenko were present.

Even more interesting would be to ask why they don't tell people how to properly set up the loudspeaker? The multi-way B&W speakers are designed with a specific listening distance and listening axes in mind. Most measurements that are seen in the mags are not performed on the correct axes which is often reflected in the measurements, e.g., the tweeter is too high for the measurement or listening axis. I received this info from a knowledgeable B&W employee. None of this critical set-up info can be found in the owner's manual! Once the speakers are set up as intended, they truly can sound magical and virtually disappear. If you have the patience with the "fussy" set-up process, it can really yield great rewards.

I don't disagree with this, but I think it deserves a bit more explanation for the uninitiated.

This particular design choice (large midrange cone, together with small "pod" tweeter) is thorny because it involves a sudden and very extreme directivity transition, from narrow beamwidth at the top end of the midrange to extremely wide beamwidth at the bottom end of the tweeter. It looks like even with these difficulties, the response of the speaker is "fairly" flat, in that it seems to fall within +/-3dB from the lower midrange to the high treble, with the exceptions being a saddle near 20kHz and a sharp dip although this is only seen in JA's full-bandwidth measurement on the tweeter and midrange axes because this is the only graph that properly captures the summation between all three drivers (the separate graphs for port, woofer, midrange, and tweeter does not give any indication of this, only the 'acoustic' crossover frequencies). The lack of consistent directivity will be the thing that has the biggest influence on how well the speaker will mate with a particular room and placement, and the overall response is not as "flat" as has been seen in other speakers, probably as a result of trying to compensate for highly variable directivity over the speaker's range.

As a designer, if I wanted to use a large midrange driver like the FST used by B&W, I would see the need to incorporate a waveguide to modify the directivity of my tweeter to match closely through the crossover region.

In the 800 series B&Ws, the contours of the "pod" tweeter blend curvaceously into the contours of the spherical-front midrange pod, helping to smooth the acoustical transition at crossover. Here, both mid driver and tweeter "see" a hard sharp edge at 90 degrees off axis. Any diffraction modeling software will show the resulting disturbances (sharp peaks and dips) that this causes in the on-axis response.

Add to this that the mid/tweet crossover is set too high: few if any 6" drivers are capable of linear output up to 4kHz, and the acoustic centers of the drivers are way more than one wavelength apart, so you'll get a lot of comb filtering effects above and below the optimum vertical listening axis. AND the tweeter's first order highpass filter is too shallow: it will still have significant output an octave below, introducing further phase anomalies and contributing to the difficulty of finding that optimum axis.

This is all basic, established knowledge, so I truly don't understand why B&W's engineers fail to take it into account! The brand has pioneered some wonderful innovations in driver and cabinet design, so why can't they get their crossovers right? I've heard maybe half a dozen B&W models over the years, and all (to my ears, anyway) required fussy positioning, and still sounded too bright and ultimately fatiguing in the treble.

To see other comparisons at this price point, Revel F208's for example. B&W's always strike me as a bit of a crap shoot compared to other brands. More sensitive to the room, to placement, to the electronics in use.

Since you also reviewed the 683 S2 a couple of years ago I am eager to hear your comparison and contrast of 702 S2 with the 683 S2. Based on the review details and measurements they seem very similar except that 702 S2 has newer drivers with better materials and a better looking cabinet and finish. I was thinking about upgrading but now not sure. Your thoughts?

Another candidate for my upgrade is Revel F208 as mentioned by brenro above. F208 appears to be better in measurements and in listening tests at almost the same price point.

There are, undoubtedly, major technical advances in the 702 S2 that go well beyond anything in the 600 series. However, I cannot offer any subjective comparative information because it has been quite a while since I heard the 683 S2 for that review and it was in my CT house/system while the 702 S2 was used in my NYC apartment.

I can't help but think that this idiosyncratic measured behaviour of the less expensive models is a deliberate design choice (I'm not going to speculate as to the reasons here). It is not difficult nor expensive to add a couple of crossover components and iron out the measured upper-midrange mess. Not ok.

Why no comparison to the similar sized and recently reviewed Monitor Audio Silver 300s? After all, they perform better on paper despite the price gap. Why not tell readers why they should consider forking over $2500 more for speakers that don't measure as well. It's no surprise that speakers of the same lineage sound similar, that's not very helpful. It's better to help us understand why one might choose B&W over the competition.

As noted above the 702 S2 was auditioned in NYC and the MA S8 and S300 were auditioned in CT. The reason is kinda lame but I am no longer willing to do heavy stuff in CT where I have to do the schlepping and lifting myself. In NYC, I have help. (The Parasound A52+ was the ton of straw and almost broke the camel's back.)

So, all I can say about all these, as a group, is that I am happy to keep the Silver8 speakers after having auditioned the 683 S2 and the Silver300 in the same room. I was not tempted to consider the more costly 702 S2 for that system.

I have a problem with multiple drivers doing the same job, as no driver is a perfect match to another, yet alone 3 of them trying to move in perfect unison, there has to be more distortion.
Maybe that's why the reviewer found the bass of the 804 D3 was more defined and tonal at the very bottom end because it only has 2 drivers doing the same job. The highest distorting component in audio is the bass speaker, here we are trying to make 3!!! of them work as a perfect single unit, it aint guna happen.

Maybe one 8" low bass and one 6" upper bass would be better again, and make the thing a 4 way.

If all three drivers are being driven in unison by a common signal, and if all three drivers are equivalent, they should move perfectly in unison. There are only a few things that could cause drivers in a common chamber with a common drive signal to move in a non-unison fashion, one of which being an extremely strong standing wave inside the enclosure that causes the pressure behind the drivers to be uneven at certain frequencies, another possibility being the existence of filtering that causes one driver to receive an out-of-phase signal, and a third being a non-functioning driver with no electrical connection to the amplifier, so it would only be moving in response to enclosure pressure. Any one of these issues would show up in a frequency response measurement as an unexpected artifact in the bass response (ripple or low level) or a mismatch between the two speakers. Even under these conditions, the response of the drivers to a transient should be proportional, and not out-of-sync with one another.

There are other things, such as electrical and mechanical damping of the drivers, the combined damping of the vented system, and a different tuning frequency, that would be much more probable in causing differences in bass character between one speaker and another.

I've never been able to measure the T&S parameters of two let alone three drivers three to be identical, even when buying "matched pairs" from a manufacture for repairs.
As I said the bass driver is the worst component for distortion, and here we are making it even worse, and nowhere does it even say these are match, which would help but not totally eliminate as the matching wouldn't be perfect.

first off, doubling the number of bass drivers should reduce the distortion at any given volume level. 2 8" woofers require half as much power to reach a given volume level as a single 8" woofer of the same model in the same sized box/driver (some speakers give each woofer its own subenclosure, some don't). Less power = less cone excursion and less voice coil heat = less distortion. Three woofers will reduce the distortion further.

second, you seem to (incorrectly) believe that drivers actually exactly match their Thiele/Small paramaters and that isn't the case in the real world except inadvertantly. All manufacturing is done to a specified tolerance, and more expensive speaker drivers tend to be made to tighter tolerances than cheaper ones. Really expensive finished speakers often have their crossovers tailored to the individual drivers - gives great sample to sample matching but makes driver replacement waaaaay more complicated and expensive... but then, if you're dropping over $50 grand on a pair of speakers you can probably afford it.

Oh, and unless otherwise noted, it's quite safe to assume the woofers are all the same because that's how pretty much everyone rolls.

Sorry to me use one "correct" driver within it's limits to do the job, and if it costs more so be it.

It comes from measuring the Thiel and Small speaker parameters on many drivers.
http://1.bp.blogspot.com/-7euZZb2iGdI/UwI5lIr62FI/AAAAAAAACQc/bIm0r1zxDco/s1600/Thiel+And+Small+Parameters+-+Alberto+A+Lopez+-.jpg

No two are perfectly alike with all measurements, and you need that here so there is absolutely no smearing effect of the drivers not moving in perfect unison stopping and starting as one. Same goes for multiple tweeters and midranges.

"No two are perfectly alike with all measurements, and you need that here so there is absolutely no smearing effect of the drivers not moving in perfect unison stopping and starting as one."

So you only listen in mono with a single speaker then? That's the logical end point of what you believe (well, really it's a single driver like a Lowther in mono). Since no two speaker drivers are identical, you're going to get that "smearing effect" regardless of how you set up your speakers whenever you have primarily mono low bass (pretty much all music outside of classical, some jazz, and some EDM).

The drop in distortion alone from adding a second woofer dwarfs the effect of slightly differing T/S parameters (and those parameters aren't even static, they change as the driver ages - especially the suspension components aging).

Any classical music lover noticed that the generation of dynamic classical music recording such as Mercury Living presence and the great hours of Decca sound engineers left the stage sometime in the 1990s replaced by a slew of anaemic recordings claiming to offer a wide sound stage, and the infinite details of the hall acoustics etc... Sadly, the dynamics of these recording were nonexistent: at best, some noise was happening down there, somewhere far and orchestral tutti barely registered, often a soup combining reflected and direct sound. From being on the podium with the conductor, listeners were relegated to the rafters. Digging information, it was explained that these recordings were mastered on B&W speakers, then the self declared new reference for "classical music".
I contend that using such low efficiency speakers and the marketing of such logs that surely could never bother any neighbour even in wafer thin walled condos has had a nefarious influence on the recording style adopted during these years by recording labels. This has contributed in turn to the revival of high dynamics recordings, the music alive that were found on the great labels mentioned above, and thus the great vinyl revival.
As for classical recordings of the 90s era, high rez downloads now available can help compensate for their lack of dynamics... and B&W churning another 90dB/w/m "softspeaker".

"Idiosyncratic" is a euphemism for inaccurate and colored but no one dares give any Bowers and Wilkins product a bad review for obvious reasons. I agree with J.P. Jackson above that the inaccuracy of the 702 is a deliberate design choice. I have owned Bowers and Wilkins speakers in the past and found that although they are decent, they have an obvious coloration, which usually consists of a recessed upper midrange and somewhat exaggerated highs. My assessment of the B and W "flavoring" is entirely consistent with the measured frequency response of 702 shown above. I had to install a 1.5 ohm resister in place of the jumper on the biwire cable jack to bring the highs down to a tolerable level. I think the B and W started out as a very good and accurate speaker but started to deviate more and more from accuracy in the quest to increase their market share. This process accelerated when they started selling their 600 and 700 series speakers at Best Buy. They have become more and more about marketing and gimmickry. John Bowers, the company's founder, is quoted as saying the ideal is a speaker that "neither adds nor subtracts" from the original performance. That is how the company started out but it is has been through several ownership changes since then. I wonder now if Mr. Bowers is rolling in his grave. If you like the coloration of the B and Ws, go for it. However, if you are looking for a more accurate speaker in the price range of the 702, you would be better off considering speakers from Revel, Focal, and Monitor Audio, to name a few. Also, the NHT C-4 is far more accurate for less than half the price.

If anyone cares to examine the response plots for tweeter and fst mid axes, clearly, the intended listening axis is roughly mid way between the two.

All B&W 700 / 800 series exhibit the same mid-treble irregularities to some extent, due to the crossover / driver integration design.

The response would be more even and uniform over a wider arc if the tweeter was inverted and "time aligned", and with higher order filters, but the B&W engineers decided on low order filters and made the decision to move the tweeter forward by a half wavelength rather than connect in reverse polarity. These design choices and reasons provided were articulated in the original Diamond 800 white paper if people care to read it.